At his home in a smart neighbourhood on the outskirts of Marseille, Michel liked to proudly display his scores of trophies from marathons from New York to Paris. "You need a certain spirit and mental focus for long-distance running," said his sister Christine.

Michel, 51, was a perfectionist with a healthy lifestyle and a distrust of prescription drugs. He had two passions in life: sport and his senior job with the French mobile and internet giant Orange. But at his desk, Michel was living a private hell that made a mockery of the company slogan "The future's bright, the future's Orange."

On France's Bastille day bank holiday, he was found dead in his bed at home by one of his sisters. He left a note stating that work was the "only reason" he killed himself, denouncing an alleged company culture of "management by terror", and constant stress. "I have become a wreck," he wrote.

Since then, his family, who do not want their surname published, has pored over every comment he made about his job, how he brought his vast workload home, his disturbed sleep.

"There was this pressure from the top to slim down operations by destabilising workers, people were undermined to the point that they got ill," his sister claimed. "He told me he was regularly sent messages from managers suggesting he find work elsewhere. Once they suggested he open a rural guesthouse. He accepted a far too heavy workload out of fear of losing his senior job. He had no other problems, no money worries, no family concerns. It's unacceptable that France Télécom [owner of the Orange brand] won't accept their share of responsibility for his death."

Michel's suicide note has become the defining message from the grave in what the French phone giant France Télécom now calls a suicide "contagion effect". In the past 18 months, 23 employees across France have killed themselves, and there have been 13 attempts. The French public is questioning how Europe's third largest mobile operator, and Europe's biggest provider of broadband internet services, has become synonymous with death and despair.

Under government pressure, France Télécom today launched negotiations with its unions over stress. This week, the company introduced helplines and new medical experts, and temporarily suspended staff relocations. But staff have begun to break their silence on their working conditions.

Workers on call-centre floors said they had to ask permission to go to the toilet or file a written explanation for going one-minute over a lunch break. Senior staff allege being bullied and being repeatedly forced to move job. Many have turned to antidepressants or taken extended sick-leave. Even workplace doctors have quit the company. One worker in Troyes, who survived stabbing himself during a meeting last week, said he felt it was his only option when told of further job moves. A woman in Metz recently found unconscious at her desk said she had tried to take her life because she was sick of being treated like a "pawn".

Outside a 1930s Orange-France Télécom building in chic western Paris, staff were coming to terms with the latest suicide. "I'm scared to speak," a worker in her 40s said. Last week, Stephanie, 32, who dealt with business customers over unpaid bills, emailed her father from her open-plan office. She wrote of her fear at changing boss – the latest in a long line of changes to her work. "I'm more than lost," she typed, before jumping from her office window. She had struggled with depression before, but was living what her father called "hell" at work. Some days she could not get up, or if she did, was in tears.

"A wave has started, now no one knows how to stop it," Patrice Diochet of the CFTC union said. "Unfortunately there will be other suicides, we're seeing a snowball effect. The directors have to completely change their management style and put back some humanity into the company. Every suicide is complex, but it's clear that recently work is what has been pushing people over the edge."

Anne, not her real name, is a close colleague of one of the latest workers to kill himself: a skilled technician at the Lannion centre in Brittany for Orange research and development. "The malaise is everywhere, from client-liaison staff who aren't allowed enough rigidly scheduled minutes to talk properly to customers, to technicians who aren't allowed the time to do thorough repairs. Only money and marketing counts, not the quality of our work. I've been moved three times. You could get a call on Friday at 11am saying you had to find somewhere else to go in the company by Monday morning. I was lucky, I clung to interesting jobs. Other highly skilled technicians ended up in call-centres, chasing unpaid bills. Even so, I've been on anti-depressants, my marriage broke up, I can't sleep at night unless I take pills."

France is particularly sensitive to workplace suicides after patterns of staff taking their lives at Renault, Peugeot and the electricity giant EDF in recent years. Some argue that the remaining public sector workers at the company are having difficulty adapting to the cut-throat ways of a privatised enterprise. But Gaëlle Urvoas, a CGT Brittany union representative, said, "It's not change, it's the way it's being handled".

Outside France, Orange's management techniques have raised eyebrows among its subsidiaries. A middle- manager at a Dublin subsection of Orange described the alleged use of "terror"and "infantile" tactics by French managers. "When a French director visited us, her associate said: 'This is going to be a longer meeting than in France because you people here aren't as afraid of the CEO as you should be'."

A sociologist, Monique Crinon, said "management by stress" was not uniquely French, but part of a new trend across Europe. After interviewing a cross-section of France Télécom and Orange staff, she identified feelings of being undervalued and "low self-esteem" running from directory inquiries, call-centre staff and sales assistants in mobile phone shops, right up to senior managers. Teams were deliberately broken up to leave workers isolated and feeling like failures in a performance-driven system. "I found normal people whose psyches had been weakened by work," she said.

One senior worker in her 50s who was demoted to work in a call-centre said she felt like she had stepped "back in time" to an era where mainly young women staff were terrorised and controlled, made to make several sales an hour from dictated scripts. "There was a lot of illness, a lot of depression, I had to leave," she said.

André Rumeau, a CGT trade unionist in his 50s, worked with Michel at Orange in Marseille. "It's shocking that a respected colleague who was so good at his job was the one who cracked," he said. "If these tragedies are to stop, things have to change at the top."

A spokesman for France Télécom said of the allegations by staff about poor work conditions: "These are complex subjects. I could very quickly find you testimony by people for whom everything is going well in their jobs. But we're facing a sequence of very dramatic events that means people are expressing themselves perhaps more freely than before.

"Many other workers don't recognise these complaints, as they have had a very good experience of the company changes over recent years. We do not deny that there have been difficulties or problems in certain places. But what is certain is that these complaints do not reflect a complete picture of the company. France Télécom has taken on board the staff concerns and launched a series of measures to deal with them."

He said Michel had been promoted and seen his salary rise as part of technological changes and his colleagues had not realised how difficult he had found this change.

Bitter fruit

France Télécom, the former state-owned monopoly, was privatised in 1997, although the French government remains the biggest shareholder, with 27% of the capital.

• In 2000, France Télécom bought Orange.

• 102,200 staff work for the company in France.

• It has 186 million customers in 30 countries worldwide.

• 65% of its workers are public sector staff, employed before privatisation.